Widely known are interactive communication systems in which a plurality of client devices are connected to one another via a relay server on the Internet (e.g., Japanese Patent Application Laid-open No. 2011-077890 and Japanese Patent Application Laid-open No. 2008-311852). A first client device out of the client devices establishes a connection with the relay server and maintains the connected state. A second client device also establishes a connection with the relay server. When the first client device, for example, outputs a message after the connection is established between the first and the second client devices and the relay server, the relay server transfers the message to the second client device. In a case where the number of client devices increases, a plurality of relay servers may be provided.
In such interactive communication systems, a certain number of relay servers out of the relay servers may possibly be shut down (referred to as scale-in). The interactive communication systems execute scale-in at times when fewer users use the systems, such as night-time, to reduce power consumption or carry out maintenance of the relay servers.
When the conventional interactive communication systems described above execute scale-in, there is such a problem that client devices connected to the relay servers to be shut down are momentarily incapable of performing communications.
Specifically, when a relay server is shut down, client devices connected to the relay server fail to perform communications if they remain in that state. The client devices need to be switched to another available relay server. After the relay servers are switched, a client device serving as a transmitter of a message and a client device serving as a receiver thereof fail to transmit and receive the message until both of them can establish a connection.